import logging
import os
from dataclasses import dataclass
from datetime import timedelta
from typing import Optional

import torch
import torch.distributed as dist
from packaging.version import Version

import ray
from ray.air._internal.device_manager import register_custom_torch_dist_backend
from ray.train._internal.utils import get_address_and_port
from ray.train._internal.worker_group import WorkerGroup
from ray.train.backend import Backend, BackendConfig
from ray.util import PublicAPI

logger = logging.getLogger(__name__)


class TorchConfigContextManager:
    def __enter__(self):
        # Set default cuda device
        if torch.cuda.is_available():
            device = ray.train.torch.get_device()
            if device.type == "cuda":
                torch.cuda.set_device(device)

    def __exit__(self, type, value, traceback):
        # Propagate exceptions if any
        return False


@PublicAPI(stability="stable")
@dataclass
class TorchConfig(BackendConfig):
    """Configuration for torch process group setup.

    See https://pytorch.org/docs/stable/distributed.html for more info.

    Args:
        backend: The backend to use for training.
            See ``torch.distributed.init_process_group`` for more info and
            valid values.
            If set to None, nccl will be used if GPUs are requested, else gloo
            will be used.
        init_method: The initialization method to use. Either "env"
            for environment variable initialization or "tcp" for TCP
            initialization. Defaults to "env".
        timeout_s: Seconds for process group operations to timeout.
    """

    backend: Optional[str] = None
    init_method: str = "env"
    timeout_s: int = 1800

    @property
    def backend_cls(self):
        return _TorchBackend

    @property
    def train_func_context(self):
        return TorchConfigContextManager


def _setup_torch_process_group(
    backend: str,
    world_rank: int,
    world_size: int,
    init_method: str,
    timeout_s: int = 1800,
):
    """Connects the distributed PyTorch backend.

    Args:
        backend: The backend (nccl, gloo, etc.) to use for training.
        world_rank: Rank of the current worker.
        world_size: Number of workers participating in the job.
        init_method: URL specifying how to initialize the process group.
        timeout_s: Seconds for process group operations to timeout.
    """
    if world_rank == 0:
        logger.info(
            f"Setting up process group for: {init_method} [rank={world_rank}, "
            f"world_size={world_size}]"
        )
    else:
        logger.debug(
            f"Setting up process group for: {init_method} [rank={world_rank}, "
            f"world_size={world_size}]"
        )
    logger.debug(f"using {backend}")

    if backend == "nccl":
        # See https://github.com/pytorch/pytorch/blob/c263bd43e8e8502d4726643bc6fd046f0130ac0e/torch/distributed/distributed_c10d.py#L803-L823 # noqa: E501
        # We do not use TORCH_NCCL_BLOCKING_WAIT due to performance overhead.
        if Version(torch.__version__) < Version("2.2.0"):
            TORCH_NCCL_ASYNC_ERROR_HANDLING_ENV_VAR = "NCCL_ASYNC_ERROR_HANDLING"
            TORCH_NCCL_BLOCKING_WAIT_ENV_VAR = "NCCL_BLOCKING_WAIT"
        else:
            TORCH_NCCL_ASYNC_ERROR_HANDLING_ENV_VAR = "TORCH_NCCL_ASYNC_ERROR_HANDLING"
            TORCH_NCCL_BLOCKING_WAIT_ENV_VAR = "TORCH_NCCL_BLOCKING_WAIT"
        if (
            TORCH_NCCL_ASYNC_ERROR_HANDLING_ENV_VAR not in os.environ
            and TORCH_NCCL_BLOCKING_WAIT_ENV_VAR not in os.environ
        ):
            logger.debug(
                f"Setting {TORCH_NCCL_ASYNC_ERROR_HANDLING_ENV_VAR}=1 to fail if NCCL collective communication operations are timing out. "  # noqa: E501
                f"To override this behavior, you can set {TORCH_NCCL_ASYNC_ERROR_HANDLING_ENV_VAR}=0."  # noqa: E501
            )
            os.environ[TORCH_NCCL_ASYNC_ERROR_HANDLING_ENV_VAR] = "1"
    elif backend == "hccl":
        register_custom_torch_dist_backend(backend)

    dist.init_process_group(
        backend=backend,
        init_method=init_method,
        rank=world_rank,
        world_size=world_size,
        timeout=timedelta(seconds=timeout_s),
    )


def _shutdown_torch(destroy_process_group=False):
    from ray.air._internal.torch_utils import get_devices

    devices = get_devices()
    if destroy_process_group:
        dist.destroy_process_group()
    if torch.cuda.is_available():
        for device in devices:
            with torch.cuda.device(device):
                torch.cuda.empty_cache()


def _set_torch_distributed_env_vars():
    # Same env vars as in
    # https://pytorch.org/docs/stable/elastic/run.html#environment-variables
    from ray.train.torch import get_device

    context = ray.train.get_context()
    os.environ["LOCAL_RANK"] = str(context.get_local_rank())
    os.environ["RANK"] = str(context.get_world_rank())
    os.environ["LOCAL_WORLD_SIZE"] = str(context.get_local_world_size())
    os.environ["WORLD_SIZE"] = str(context.get_world_size())
    os.environ["NODE_RANK"] = str(context.get_node_rank())

    # Makes sure Hugging Face Accelerate uses the correct device
    device = get_device()
    os.environ["ACCELERATE_TORCH_DEVICE"] = str(device)


class _TorchBackend(Backend):
    share_cuda_visible_devices: bool = True

    def on_start(self, worker_group: WorkerGroup, backend_config: TorchConfig):
        if dist.is_available():
            # Set the appropriate training backend.
            if backend_config.backend is None:
                if worker_group.num_gpus_per_worker > 0:
                    backend = "nccl"
                else:
                    backend = "gloo"
            else:
                backend = backend_config.backend

            master_addr, master_port = worker_group.execute_single(
                0, get_address_and_port
            )
            if backend_config.init_method == "env":

                def set_env_vars(addr, port):
                    os.environ["MASTER_ADDR"] = addr
                    os.environ["MASTER_PORT"] = str(port)

                worker_group.execute(set_env_vars, addr=master_addr, port=master_port)
                url = "env://"
            elif backend_config.init_method == "tcp":
                url = f"tcp://{master_addr}:{master_port}"
            else:
                raise ValueError(
                    f"The provided init_method ("
                    f"{backend_config.init_method}) is not supported. Must "
                    f"be either 'env' or 'tcp'."
                )

            setup_futures = []
            for i in range(len(worker_group)):
                setup_futures.append(
                    worker_group.execute_single_async(
                        i,
                        _setup_torch_process_group,
                        backend=backend,
                        world_rank=i,
                        world_size=len(worker_group),
                        init_method=url,
                        timeout_s=backend_config.timeout_s,
                    )
                )
            ray.get(setup_futures)
        else:
            raise RuntimeError("Distributed torch is not available.")

    def on_shutdown(self, worker_group: WorkerGroup, backend_config: TorchConfig):
        worker_group.execute(
            _shutdown_torch,
            destroy_process_group=len(worker_group) > 1,
        )

    def on_training_start(
        self, worker_group: WorkerGroup, backend_config: BackendConfig
    ):
        worker_group.execute(_set_torch_distributed_env_vars)
